What has happened to my Disability Premium of £31?

Since being transferred to ESA from Incapacity Benefit some months ago and notifying Housing Benefit as advised to do by the website I suddenly noticed that after re assessement the monthly rent cheques were only 50%of the rent instead of the previous 85%.!
On studying the letter notification it appears that a HB component called "Disability Premium of £31"(p.w)is missing.
Is this a mistake or is it that "Disability Premium"was only paid when connected to the now obsolete Incapacity benefit?
In other words ESA WRAG Claimants do not now receive it.
If so this is a bit cheeky as essentially although ESA WRAG Claimants have been re categorised they are essentially now classed as "fit"for these purposes hence the withdrawl of Disability Premium from all new ESA WRAG Claaiments?
Rent is c.100 pounds a week for tiny bedsit share toilet bath with 6 others
and this below the belt blow means only 50 pounds now will come from HB.
The rest will come out of ESA as longa s that lasts though with sanctions not long
leaving a shortfall that means one is worse off than on JSA!
Can you elaborate please?